US patent application publication no. US2010/0167441, entitled, Method of Manufacturing a Light Emitting, Photovoltaic or Other Electronic Apparatus and System, is assigned to the present assignee and incorporated herein by reference. The publication describes various techniques to form light emitting diode (LED) sheets and photovoltaic (PV) panels using arrays of semiconductor micro-diodes. In particular, the PV panels are comprised of microspheres and may be on the order of 20-40 microns in diameter. Several methods of manufacturing silicon spheres are known and include forming spheres from molten silicon in a drop tower, patterning silicon particle agglomerates on a substrate and melting them to form spheres by surface tension, or dropping powder through a plasma reactor.
In the prior art, a relatively large PV cell can be fabricated with all the micro-diodes connected in parallel. The voltage generated by each PV cell is about 0.6 volts, and the current depends on the size of the cell. Multiple PV cells can be separately manufactured and then the individual PV cells can be mounted on a much larger common substrate, such as having an area of several square feet to form a module. Tabbing and stringing to the cells is done to connect the individual PV cells in series to increase the voltage of the module. This process is slow and expensive, and the solder joints used to connect to each cell are susceptible to failure, resulting in power loss during the operating lifetime of the panel. Integration of bypass diodes is also done at the module level in a serial process, and typically, several cells rely on a single bypass diode to save on cost. Moreover, this technique of increasing the voltage is limited since there is a linearly increasing cost to separately mount more and more PV panels on a large substrate and connect them in series.
What is needed is an inexpensive technique to form a single PV module, of any size, using printed silicon micro-diodes, where the single PV module is made up of many small PV cells connected in series with printed bypass diodes connected in parallel. This also enables higher voltages, such as exceeding 200 volts, to be generated by a single PV panel. This ultimately lowers the total balance of system cost of a photovoltaic array.